1. Field of the Invention
This invention relates, in general, to electrical apparatus and, more specifically, to vaporization cooled electrical inductive apparatus.
2. Description of the Prior Art
Electrical inductive apparatus, such as power transformers, are commonly either force-cooled by pumping an insulating dielectric fluid or other coolant through ducts in the windings or are cooled by natural circulation of the coolant upwardly through the ducts in the windings by the convection mechanism. The coolant absorbs heat from the adjacent surfaces of the core and coils and, in turn, dissipates this heat to the ambient air as it flows through radiators. Since the amount of coolant flowing past the surfaces of the core and windings determines the amount of heat that is removed, duct sizes ranging from 1/8 inch to 3/8 inch in thickness for liquid coolants and from 1/4 inch to 1 inch for gas (i.e. air) cooling mediums have been employed to ensure an adequate supply of coolant across the surfaces of the core and windings.
Vaporization cooling systems have also been proposed for electrical inductive apparatus which utilize a two-phase dielectric fluid having a boiling point within a normal operating temperature range of the electrical inductive apparatus. The dielectric fluid, which is used in relatively small amounts, is supplied to the electrical inductive apparatus in its liquid state, whereon it evaporates as it contacts the heat producing members and removes heat in quantities equal to the latent heat of vaporization of the dielectric fluid. The resulting vapors are then condensed and reapplied to the heat producing elements in a continuous cycle. In order for vaporization cooling systems to be efficient, it is necessary that the dielectric fluid uniformly wet or form a thin film over the exposed surfaces of the core and windings. Various liquid distribution means have been employed in the prior art to ensure the uniform wetting of all surfaces and thereby avoid the formation of hot spots within the winding or core of an electrical inductive apparatus. It has also been necessary to provide an adequate circulation rate of the dielectric fluid in order to maintain a constant film or coat of liquid dielectric on the exposed surfaces of the winding and core of the electrical inductive apparatus. Prior art vaporization cooled electrical inductive apparatus have employed ducts or fluid flow passages through the windings of similar sizes as those employed for liquid or gas cooled apparatus. However, the use of ducts or fluid flow passages having conventional widths ranging from 1/8 inch to 1 inch present several disadvantages or inefficiencies when used in vaporization cooled electrical inductive apparatus, such as transformers. The relatively low viscosity of the vaporizable fluids commonly used causes the dielectric fluid to form rivulets or streams as it flows through ducts having widths within the aforementioned size range which thereby prevents the dielectric fluid from uniformly wetting or coating both wall surfaces of the ducts. Furthermore, a considerable amount of the dielectric fluid flows completely through the ducts without being vaporized which not only increases the amount of dielectric fluid required to adequately cool the electrical inductive apparatus, but also requires increased circulation rates in the pumps and devices normally used to distribute the dielectric fluid over the electrical apparatus.
Thus, it is desirable to provide a vaporization cooled electrical apparatus having improved cooling efficiency compared to prior art apparatus of a similar type. It is also desirable to provide a vaporization cooled electrical apparatus wherein the vaporizable fluid uniformly coats the exposed conductor surfaces as it flows through the fluid flow passages in the electrical apparatus. Finally, it is desirable to provide a vaporization cooled electrical apparatus in which improved coding efficiency and uniform coating of the conductor is achieved with a smaller amount of vaporizable fluid than that normally used in prior art apparatus of this type.